This invention relates to the field of intravascular catheters, and more particularly to a catheter having a shaft formed in part of a liquid crystal polymeric material (LCP).
Balloon catheters generally comprise a catheter shaft with a balloon on the distal end of the shaft, and are used in a number of procedures, such as percutaneous transluminal coronary angioplasty (PTCA). In PTCA the balloon catheter is used to restore free flow in a clogged coronary vessel. The catheter is maneuvered through the patient""s tortuous anatomy and into the patient""s coronary anatomy until the balloon is properly positioned across the stenosis to be dilated. Once properly positioned, the balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 4 atm) to reopen the coronary passageway.
High strength materials are commonly required in the design of catheter components. For example, to improve catheter maneuverability, the catheter shaft is typically provided with a relatively stiff proximal shaft section and a relatively flexible distal shaft section. The stiffened proximal shaft section provides greater push to the catheter which facilitates advancement over a guidewire. The stiffness also provides greater torqueability so that torque applied to the proximal end of the catheter extending outside of the patient results in rotation of the distal tip of the catheter. However, for overall catheter performance, the proximal shaft stiffness must be balanced against the need to maintain a low profile and shaft flexibility. Stiffened proximal shaft sections are typically formed from stainless steel hypotube and polymeric materials, although pseudoelastic or elastic NiTi alloys may also be used. However, these prior art materials have the drawbacks of high cost, or inadequate performance by being overly stiff in the case of hypotubing or inadequately stiff in the case of polymeric shafts.
Therefore, what has been needed is a balloon catheter with a stiffened shaft section having improved strength characteristics. The present invention satisfies these and other needs.
The invention is directed to a catheter which has at least part of the shaft thereof formed of a liquid crystal polymeric material. In a presently preferred embodiment, the catheter shaft is formed of a polymer formulation of at least 50 percent by weight liquid crystal polymeric material. In one embodiment, the liquid crystal polymeric material is blended with a non-liquid crystal polymeric material to form a polymer blend (hereafter, the LCP blend). In a presently preferred embodiment of the LCP blend, the LCP blend has at least 50 percent by weight and less than 100 percent by weight of the liquid crystal polymeric material. There are many suitable liquid crystal polymers that may be used, and a presently preferred example is VECTRA sold by Hoechst-Celanese. The non-liquid crystal polymeric material used in the LCP blend may be any extrudable thermoplastic polymer, and presently preferred examples are polyester copolymers such as HYTREL available from Du Pont de Nemours, and PEEK available from Victrex.
A catheter shaft formed from the LCP blend of the invention has improved stiffness. The LCP acts as reinforcement in the polymer matrix, similar to braided fiber reinforcements used in catheter shaft construction but at significantly improved cost and ease of manufacture.
Liquid crystal polymers exhibit crystalline behavior in the liquid phase such that the liquid phase molecules retain some of the orientational order of the solid phase. The molecular orientation improves the strength of a polymeric component in the direction of orientation. The extent of molecular orientation can be expressed in terms of the aspect ratio, which is the ratio of the length of the liquid crystal polymer fibrils to the diameter of the fibrils. The aspect ratio is a factor of the draw-down ratio, which is the ratio of the diameter of the die to the diameter of the finished extrudate, used during extrusion. Liquid crystal polymers can be made to solidify after extrusion with an even greater degree of molecular orientation than ordinary polymers, and thus can be used to form ultra high strength articles. However, the high molecular orientation may result in disadvantageous characteristics in a catheter shaft, such as a low elongation and little ability to withstand loads applied transverse to the orientation direction. These disadvantages are avoided by the polymer blend of the invention. Thus, the catheter shaft of the invention formed of a polymer blend of at least 50% by weight liquid crystal polymeric material with a non-liquid crystal polymeric material provides improved shaft strength and stiffness characteristics.
One presently preferred embodiment of the invention is a dilatation catheter which has an elongated catheter shaft with a relatively stiff proximal section formed of the LCP blend and a relatively flexible distal section and an inflatable dilatation member on a distal portion of the catheter. Conventional catheter design may be used, including over the wire, fixed wire and rapid exchange designs, having a single shaft with dual lumens or a multimembered shaft with inner and outer tubular members.
A catheter shaft formed from the polymer blend of the invention has improved strength, stiffness, and kink resistance. These and other advantages of the invention will become more apparent from the following detailed description of the invention and the accompanying exemplary drawings.